Don't Idle a Deisel..... Why?

[chuntag95]

Okay, I will ask the stupid question, that I know someone knows the answer too. I have seen and heard to never idle a deisel more than 10 minutes. It even says something about it in the owners manual. Why? Part II: How does the high idle switch negate this (see questions one's answer) problem? I let my truck idle when cold to warm it up and sometimes it might be 15-20 minutes. I want to make sure I am not hurting it and would gladly add the high idle switch. Just want to know the skinny.

[MartyB]

While I will not quote my specs to be correct, but the reason to not idle, is 1 hour of idling is the ~ equal to 1000 miles of driving IIRC.
There was a good thread about a year ago in the 6.5 members area, again IIRC with the exact hour = to x miles of driving formula.
Also most engines will warm up quicker and more thorough, if started and driven at slow to mederate speeds for a bit until the engine guage is at normal temps.

"On Edit"
Here is a link to the thread I was remembering
http://forum.62-65-dieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=1&t=001129&p=
How do I hyper link this? :confused: It is not working! :mad:

[ 10-11-2002: Message edited by: MartyB ]</p>

[mackey_62]

I can't explain the physics behind this but.... "Excessive" idling will dilute your engine oil with fuel. IMO at higher idle RPM's the fuel is more completly combusted, thus not causing fuel-wash. Again, I'm not a diesel expert, but have been told by those more knowledgable that if idling is necesary, it should be done at a higher RPM. Hope this helps, maybe someone else will shed some more light.

[jbplock]

One reason not to idle a Diesel in New York State is so that you don't get a ticket. It's part of the Diesel emision laws. I don't remember the exact time limit but it's something like 5 minutes. Doesn't seem like it's enforced though.

[DieselDadd1]

I think the reason why you should'nt let a diesel idle,is because at idle,the connecting rods aren't able to throw a decent amount of oil onto the cylinder walls.Thus,engine wear increases and fuel dilutes the engine oil.Sure,on cold starts it's okay to let it idle for 2-3 minutes,then your able to drive the vehicle away.

[AKDmax]

Not idling for long periods may work where it's warm (above -10) most of the time. Go to any parking lot up here in November-February and all the diesels are idling. Sure it's probably not good for this or any other engine, but a cold start is much worse than a long idle. Running synthetic and changing often would be a good idea during winter months. Disclaimer: I'm not an engineer, just my opinion and observation. The high idle will bring your temps up faster so the 20 minute wait shouldn't be needed. Best and one of the cheapest mods you'll ever do on your truck. Go to a truck stop and count the trucks idling vs. not. Not sure why the big rigs don't shut down. You know the saying opinions are like ********, everyone has one.

[Jim Bob]

I've heard the business about unburned fuel "washing down" the cylinder walls at idle and increasing wear, too. I think one other reason the owner's manual says not to leave an engine idling is that if something went wrong (coolant system failure, loss of oil pressure, etc.etc.) you wouldn't be there to shut the engine down. Pretty unlikely, but that's the way the owner's manual writers think!

Unless you're in real winter weather, just starting the engine, letting the oil pressure stabilize and then driving with light throttle and keeping it below 40 mph is going to warm the engine up much faster than idling it and save fuel. I absolutely will not get on a road where I have to go over 40 mph until the engine is reasonably well warmed up. Also, since I'm retired, I try to stay as far away from cold weather as possible!

[Professor]

Jim Bob,

Failure is a possibility. I started my (gas)Suburban one very cold morning and left it running to defrost the windows a bit. I came out about 10 minutes later and found myself walking in 5w30 Mobil 1. The seal between the stock oil filter mount and the block failed and dumped about 3 quarts of oil on the ground. I think the low oil pressure would have killed the fuel pump, but I

[Vaughn MacKenzie]

This subject has been discussed many times on TDR. Some points:

Once an engine is warmed up past 140F, there is no harm at all at letting it idle for a period of time. This is especially true if it's not that could out. But, why waste your fuel? If you aren't going to be going anywhere for more than 5-10 minutes, shut if off.

It is not a good idea to warm up your diesel by starting it cold in the morning then letting it run. This kind of idling is where incomplete combustion and carbon/deposits and cylinder washdown occurs. The best thing: Let it idle only for a minute or so to get oil circulating, then head out, driving gently for the first couple of miles.

If you are in severe cold and not going to be driving for awhile, better to shut it down unless there is danger of not being able to restart. In this case, Cummins for example recommends revving the engine up to higher RPM levels for specified numbers of minutes, in stages, up to 3300rpm, and repeat this cycle every hour or so (I don't recall the exact details).

I've heard stories about guys breaking valve heads off due to carbon buildup idling in the winter too much. When you have fuel that is basically smoldering in the cylinders, carbon buildup happens very fast. And, given the very tight clearances in the combustion chamber, there is not a lot of room for a margin of safety.

Vaughn

[stutzismydog]

Do you let your Warm engine IDLE as part of the turbo cool down after coming to a stop while pulling a load

[IndigoDually]

I idle my truck until the egt's are under 300 degrees. This is especially important on a turbo motor. If You shut down a turbo when it is hot the oil in the bearings will be cooked into sludge and eventually clog the oil passages and cause a bearing failure. The turbo on a D-Max is also liquid cooled and it cools down even faster and runs cooler. I have always idled the motor for a little while when pulling and usuaully just driving down the residential road that You live on is enough to cool down and stabilize the turbo temps since driving 25 mph or so is not much of a load on the motor.

John

[pilot2bombardier]

I idle my I-6 Cats all the time ie. Winter for heat/ Summer-for A/C. I raise the idle via cruise control about 300-500rpm for better oiling. never had a problem...